The G. L. Brown lecture. Adventures in anaesthesia

The results presented in this lecture show that anaesthetic agents impede the transfer of information from the periphery to the cerebral cortex. This is shown both as a reduction in the amplitudes of the initial positive and negative waves of the cerebral cortical response evoked by simulation of the periphery and as an increase in the latency of this response. This effect is most probably a prime effect of anaesthesia since (a) it is common to all the anaesthetics used, (b) the potency of the anaesthetics is directly proportional to their lipid solubility, and (c) the effect is reversed by high ambient pressures. The major site at which information transfer is most susceptible to the action of anaesthetics is at the level of the ventrobasal thalamus, although the cells in cortical layer V also appear to have an enhanced susceptibility to anaesthetic action. This latter observation is seen both in whole animal and cortical slice preparations. None the less, the first site of synaptic transfer at which anaesthetics exert a profound effect is upon the monosynaptically generated responses of ventrobasal thalamic neurones to cuneothalamic input. A possible mechanism of action for anaesthetic agents acting at this site would be upon a hypothetical cortico-thalamic-reticular-thalamic loop with the theoretical ability to control the responsiveness of the ventrobasal thalamic cells. This action was proposed both from the activity of neurones in response to anaesthetic agents and the anatomical arrangement seen in the thalamus. The thalamic reticular nucleus is a curved sheath of cells situated between the internal capsule and the external medullary lamina, capping and bounding laterally the specific nuclei of the dorsal thalamus. There is both anatomical and physiological evidence that the thalamic reticular nucleus comprises part of the thalamic reticular formation: its cellular structure also resembles that of the brain stem regions of the reticular formation (Ramon-Moliner, 1975). Early degeneration and Golgi studies showed that ascending fibres from the medial parts of the pontine and mesencephalic components of the brain stem reticular formation innervated the thalamic reticular nucleus ventrally, by penetrating the zona incerta, and dorsally, via the intralaminar and dorsal thalamic nuclei (Scheibel & Scheibel, 1958). These observations have been confirmed and extended more recently and it appears that the major innervation of the thalamic reticular nucleus occurs via the ventral route which follows the entire course of the reticular nucleus. No fibres ascending from the dorsal column lemniscal system, the spino-cervico-lemniscal system or the spinothalamic tract have been observed to terminate within the thalamic reticular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)     

2型糖尿病大鼠心室肌细胞离子通道功能和表达变化

目的:探讨2型糖尿病大鼠心室肌细胞离子通道电流及其相关蛋白表达的改变。方法:采用Zucker糖尿病肥胖(Zucker diabetic fatty,ZDF)大鼠建立2型糖尿病大鼠模型,Zucker瘦型(Zucker lean,ZL)大鼠为对照组。采用急性酶解法分离大鼠单个心室肌细胞,采用全细胞膜片钳技术记录其动作电位、L型钙通道电流(I_Ca-L)及瞬时外向钾电流(I_to)的变化;提取大鼠心肌组织蛋白,采用Western blot检测心肌细胞肥大标志物β-肌球蛋白重链(β-myosin heavy chain,β-MHC)和心房钠尿肽(atrial natriuretic peptide,ANP),以及L型钙通道(Cav1.2)和钾通道(Kv4.3)的蛋白表达水平。结果:用高脂饮食诱导ZDF大鼠成功建立2型糖尿病模型;与ZL大鼠相比,ZDF大鼠心室肌细胞的动作电位时程显著延长,I_Ca-L和I_to密度显著降低[峰值分别为(?5.96±0.37)pA/pF vs(?4.92±0.30)pA/pF,(12.43±0.86)pA/pF vs(7.48±0.58)pA/pF,均P<0.05];与ZL大鼠相比,ZDF大鼠心肌组织中β-MHC和ANP的表达水平明显增加,伴有Cav1.2和Kv4.3蛋白表达下降(P<0.05)。结论:与ZL大鼠相比,2型糖尿病大鼠心肌细胞肥大,心室肌细胞动作电位时程延长,I_Ca-L和I_to密度及其相关蛋白表达水平降低,提示糖尿病大鼠心室肌细胞发生电生理重构。     

Inhibitory regulation of acid-sensing ion channel 3 by zinc

Acid-sensing ion channel 3 (ASIC3) is a proton-gated, voltage-insensitive Na⁺ channel that is expressed primarily in peripheral sensory neurons and plays an important role in pain perception, particularly as a pH sensor following cardiac ischemia. We previously reported that ASIC3 currents are not affected by zinc at nanomolar concentrations. In this study, we examined the potential role of micromolar zinc in the regulation of ASIC3. In CHO cells expressing ASIC3, we found that ASIC3 currents triggered by dropping the pH from 7.4 to 6.0 were inhibited by pretreatment with zinc in a concentration-dependent manner; the half-maximum inhibitory concentration of zinc was 61 μM. ASIC currents activated by a relatively small drop in pH from 7.4 to 7.2 or 7.0 were also subject to inhibition by zinc. The inhibition was fast and pH independent, and occurred within a relatively narrow range of zinc concentrations between 30 and 300 μM. Further, increasing extracellular Ca²⁺ concentrations from 2 to 10 mM failed to affect inhibition of ASIC3 currents by zinc. Experimentally elevating intracellular zinc levels did not affect the inhibition of ASIC3 currents by equal concentrations of extracellular zinc, and modification of cysteine or histidine residues had no effect on the inhibition of ASIC3 currents by zinc. These collective results suggest that zinc is an important regulator of ASIC3 at physiological concentrations, that zinc inhibits ASIC3 in a pH- and Ca²⁺-independent manner, and that inhibition of ASIC3 currents is dependent upon the interaction of zinc with extracellular domain(s) of ASIC3.     

The mammalian KIR2.x inward rectifier ion channel family: expression pattern and pathophysiology

Inward rectifier currents based on K_IR2.x subunits are regarded as essential components for establishing a stable and negative resting membrane potential in many excitable cell types. Pharmacological inhibition, null mutation in mice and dominant positive and negative mutations in patients reveal some of the important functions of these channels in their native tissues. Here we review the complex mammalian expression pattern of K_IR2.x subunits and relate these to the outcomes of functional inhibition of the resultant channels. Correlations between expression and function in muscle and bone tissue are observed, while we recognize a discrepancy between neuronal expression and function.     

The Wellcome Prize Lecture. Visual signals in the retina: from photons to synapses

The ability to see the world around us is an immediate and striking example of the abilities of the nervous system, and perhaps for this reason, vision is one of the most intensively studied aspects of brain function (Hubel, 1995). This paper examines some of the earliest steps in vision occurring in the retina (Dowling, 1987; Rodieck, 1998).     

The symptoms of chronic fatigue syndrome are related to abnormal ion channel function

The pathogenesis of chronic fatigue syndrome (CFS) is unknown but one of the most characteristic features of the illness is fluctuation in symptoms which can be induced by physical and/or mental stress. Other conditions in which fluctuating fatigue occurs are caused by abnormal ion channels in the cell membrane. These include genetically determined channelopathies, e.g. hypokalemic periodic paralysis, episodic ataxia type 2 and acquired conditions such as neuromyotonia, myasthenic syndromes, multiple sclerosis and inflammatory demyelinating polyneuropathies. Our hypothesis is that abnormal ion channel function underlies the symptoms of CFS and this is supported also by the finding of abnormal cardiac-thallium201 SPECT scans in CFS, similar to that found in syndrome X, another disorder of ion channels. CFS and syndrome X can have identical clinical symptoms. CFS may begin after exposure to specific toxins which are known to produce abnormal sodium ion channels. Finally, in CFS, increased resting energy expenditure (REE) occurs, a state influenced by transmembrane ion transport. The hypothesis that ion channels are abnormal in CFS may help to explain the fluctuating fatigue and other symptoms.     

The physiological regulation of toll-like receptor expression and function in humans

Eleven mammalian toll-like receptors (TLRs 1–11) have been identified to date and are known to play a crucial role in the regulation of immune responses; however, the factors that regulate TLR expression and function in vivo are poorly understood. Therefore, in the present study, we investigated the physiological regulation of TLR expression and function in humans. To examine the influence of diurnal rhythmicity on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers ( n = 8) at time points coinciding with the peak and nadir in the endogenous circulating cortisol concentration. While no diurnal rhythmicity in the expression of TLRs 1, 2, 4 or 9 was observed, the upregulation of costimulatory (CD80 and CD86) and antigen-presenting (MHC class II) molecules on CD14⁺ monocytes following activation with specific TLR ligands was greater ( P < 0.05) in samples obtained in the evening compared with the morning. To examine the influence of physical stress on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers ( n = 11) at rest and following 1.5 h of strenuous exercise in the heat (34°C). Strenuous exercise resulted in a decrease ( P < 0.005) in the expression of TLRs 1, 2 and 4 on CD14⁺ monocytes. Furthermore, the upregulation of CD80, CD86, MHC class II and interleukin-6 by CD14⁺ monocytes following activation with specific TLR ligands was decreased ( P < 0.05) in samples obtained following exercise compared with at rest. These results demonstrate that TLR function is subject to modulation under physiological conditions in vivo and provide evidence for the role of immunomodulatory hormones in the regulation of TLR function.     

Hypoxic inhibition of respiratory neural regulation in anesthetized rats.

To determine the neural mechanism of hypoxic respiratory inhibition, discharge patterns of efferent phrenic (Phr), vagal superior laryngeal (Xsl), and vagal pharyngeal (Xphar) nerves were analyzed during systemic hypoxia in the urethane-anesthetized, vagotomized and artificially ventilated rat. In the carotid sinus nerve (CSN) intact rat, moderate hypoxia (end-tidal Po2, 40-50 mmHg) caused an initial increase in respiratory activity which was followed by inhibition due to reduction in respiratory frequency (f). The decrease in f was associated with prolongation of decremental Xphar expiratory (E) activity and retardation of the onset of inspiratory (I) activity. Integrated peak Phr or Xs1 I and Xphar E activities remained augmented during respiratory inhibition. After bilateral CSN section, moderate hypoxia produced an extreme reduction in f due to delayed onset of I activity and a strong reduction in the Xphar E activity. Phr and Xs1 I activities were little affected, and changes in inspiratory time were small. These results suggest that hypoxia centrally inhibits the process of initiating the onset of rhythmic I activity and the activity of decremental Xphar E motoneurons. Carotid chemoreceptor stimulation was inadequate to offset the central inhibitory effect of hypoxia on the onset of I activity.     

Modulation of glycine-activated ion channel function by G-protein betagamma subunits

Glycine receptors (GlyRs), together with GABA(A) and nicotinic acetylcholine (ACh) receptors, form part of the ligand-activated ion channel superfamily and regulate the excitability of the mammalian brain stem and spinal cord. Here we report that the ability of the neurotransmitter glycine to gate recombinant and native ionotropic GlyRs is modulated by the G protein betagamma dimer (Gbetagamma). We found that the amplitude of the glycine-activated Cl- current was enhanced after application of purified Gbetagamma or after activation of a G protein-coupled receptor. Overexpression of three distinct G protein alpha subunits (Galpha), as well as the Gbetagamma scavenger peptide ct-GRK2, significantly blunted the effect of G protein activation. Single-channel recordings from isolated membrane patches showed that Gbetagamma increased the GlyR open probability (nP(o)). Our results indicate that this interaction of Gbetagamma with GlyRs regulates both motor and sensory functions in the central nervous system.     

Dynamic of ion channel expression at the plasma membrane of cardiomyocytes

Cardiac myocytes are characterized by distinct structural and functional entities involved in the generation and transmission of the action potential and the excitation-contraction coupling process. Key to their function is the specific organization of ion channels and transporters to and within distinct membrane domains, which supports the anisotropic propagation of the depolarization wave. This review addresses the current knowledge on the molecular actors regulating the distinct trafficking and targeting mechanisms of ion channels in the highly polarized cardiac myocyte. In addition to ubiquitous mechanisms shared by other excitable cells, cardiac myocytes show unique specialization, illustrated by the molecular organization of myocyte-myocyte contacts, e.g., the intercalated disc and the gap junction. Many factors contribute to the specialization of the cardiac sarcolemma and the functional expression of cardiac ion channels, including various anchoring proteins, motors, small GTPases, membrane lipids, and cholesterol. The discovery of genetic defects in some of these actors, leading to complex cardiac disorders, emphasizes the importance of trafficking and targeting of ion channels to cardiac function. A major challenge in the field is to understand how these and other actors work together in intact myocytes to fine-tune ion channel expression and control cardiac excitability.     

The nutritional regulation of T lymphocyte function.

Prostaglandin (PG) E1 plays a major role in the regulation of thymus development and T lymphocyte function and the evidence for this is reviewed. The production of PGE1 is dependent on nutritional factors with linoleic acid, gamma-linolenic acid, pyridoxine, zinc and vitamin C playing key roles. Inadequate intake of any one of these will lead to inadequate PGE1 formation and defective T lymphocyte function. Megadoses of any one are likely to be only minimally effective in the absence of adequate intakes of the others. By careful attention to diet it should be possible to activate T lymphocyte function in the large number of diseases including rheumatoid arthritis, various auto-immune diseases, multiple sclerosis, and cancer in which such function is defective. It is possible that T lymphocytes may require both endogenous and exogenous PGE1 in order to function adequately. It is therefore of particular interest that many cancer cells and virally infected cells are unable to make PGE1 because they cannot convert linoleic acid to gamma-linolenic acid. The direct provision of gamma-linolenic or dihomo-gammalinolenic acids in these situations is worthy of full investigation.     

敲低IK1钾通道抑制ClC-3氯通道的表达和功能

 目的: 探讨ClC-3氯通道是否为IK1钾通道的调节靶点,重点研究鼻咽癌细胞IK1钾通道对ClC-3氯通道功能及蛋白表达的影响。方法: 采用siRNA转染技术抑制低分化鼻咽癌上皮细胞(CNE-2Z) IK1 基因的表达;real-time PCR技术检测ClC-3 mRNA的表达;Western blot检测ClC-3的蛋白表达;细胞免疫荧光结合激光共聚焦显微镜技术检测ClC-3和IK1蛋白在细胞内分布;全细胞膜片钳记录细胞氯电流。结果: IK1 siRNA可以成功转染CNE-2Z细胞,有效抑制鼻咽癌细胞IK1钾离子通道的表达;用IK1 siRNA抑制鼻咽癌细胞IK1钾离子通道的表达后, ClC-3的mRNA表达上调而ClC-3蛋白却表达减少:在低分化鼻咽癌上皮细胞,低渗刺激可激活氯通道,产生一个较大的氯电流,在成功转染IK1 siRNA的细胞,此氯电流明显减弱。结论: 敲低IK1钾离子通道可抑制ClC-3氯离子通道的表达和功能。     

Regulation of acid-sensing ion channel 1a function by tissue kallikrein may be through channel cleavage

When searching for a target object presented in a context of other, irrelevant objects, the dissimilarity between target and surrounding context elements as well as the similarity between context elements themselves affect search efficiency. The present functional imaging study explored the cortical mechanisms involved in processing the same target when surrounded by context arrangements of varying homogeneity. Results showed that brain activity increased in the precuneus, cingulate gyrus, and the middle temporal gyrus as context homogeneity and local feature contrast increased. Contexts with low homogeneity and local feature contrast, compared to contexts with high homogeneity and local feature contrast, increasingly involved areas near the corpus callosum and the medial frontal gyrus. The results support the assumption that contextual grouping and local target detection both contribute to perform the visual search task.     

Regulation of acid-sensing ion channel 1a function by tissue kallikrein may be through channel cleavage

Recently, we have demonstrated that serine protease tissue kallikrein (TK) can protect cortical neurons against ischemia-acidosis/reperfusion-induced injury, and that this effect might be mediated by acid-sensing ion channels (ASICs). However, little is known about how TK regulates the function of ASICs. Here we provided evidence that the regulation of ASIC1a function by TK was probably correlated with its cleavage. High concentration of TK (3 μM) partially cleaved the extracellular loop of ASIC1a, followed by a marked decrease of LDH release and an increase of cell survival at pH 6.2. Pretreatment with a protease inhibitor aprotinin inhibited the cleavage of ASIC1a and prevented functional regulation by TK. However, the cleavage of ASIC2a, which was not functionally modified by TK, was not observed. Therefore, we propose that the limited proteolysis of extracellular loop within ASIC1a might be one of the potential regulatory mechanisms of ASIC1a function by TK.